1. Field of the Invention
The present invention relates to an input device for various electronic equipment and a method for detecting a switch of the input device.
2. Background Art
Recently, automobiles equipped with an input device such as a steering switch in the vicinity of a steering wheel have been developed. A user can operate electronic equipment such as an audio system and an air conditioner by operating the input device by the finger in a state in which the user holds the steering wheel. In such automobiles, an input device capable of reliable operation without an operation error has been demanded.
FIG. 3 is a circuit block diagram of a conventional input device. FIG. 4 is a front view of a steering wheel using the conventional input device.
A plurality of resistors 1, 2, and 3 such as a fixed resistor are mounted on a wiring board (not shown), and connected in series. A plurality of wiring patterns are formed on the upper and lower surfaces of the wiring board. Furthermore, switches 4, 5, and 6 such as a push switch are mounted on the wiring board. One end of switch 4 is connected between resistor 1 and resistor 2, one end of switch 5 is connected between resistor 2 and resistor 3, and one end of switch 6 is connected to resistor 3, respectively, by the wiring pattern. The other ends of switches 4, 5, and 6 are grounded. Thus, a resistor divider is formed.
Control unit 7 such as micro computer is mounted on the wiring board. Resistor 1 and control unit 7 are connected to input terminal 8 such as a connector by the wiring pattern. Control unit 7 is connected to output terminal 9 such as a connector by the wiring pattern.
To the other input terminal 8A provided on the wiring board, resistors 1A, 2A, and 3A are connected in series. Switches 4A, 5A, and 6A are respectively connected to resistors 1A, 2A, and 3A to form a resistor divider. Control unit 7 is connected to input terminal 8A.
Input device 10 configured above is attached to right and left spokes 20B between steering wheel 20 and center pad 20A as shown in FIG. 4 and installed in an automobile. An air bag or the like is housed in pad 20A. A plurality of push buttons 31 to 33 and push buttons 41 to 43 each showing a different function are attached to switches 4 to 6 and switches 4A to 6A, respectively.
Furthermore, as shown in FIG. 3, input terminal 8 of input device 10 is electrically coupled to drive unit 24 of electronic equipment 22 such as an audio system via diode 25. Diode 25 is connected in series to resistor 23. Drive unit 24 is, for example, micro computer coupled to a power supply such as a battery via resistor 23.
Furthermore, input terminal 8A is electrically coupled to drive unit 24A of electronic equipment 22A such as an air conditioner via diode 25A. Drive unit 24A is coupled to a power supply via resistor 23A. Output terminal 9 is electrically coupled to display device 26 such as a liquid crystal display device installed in the front part of a driver's seat by a connector, a lead wire (not shown), or the like.
Next, an operation of input device 10 is described. Herein, resistance values of diodes 25 and 25A may vary for each equipment, which may cause a voltage drop. Firstly, a case in which the voltage drop by diodes 25 and 25A is small and negligible is described.
A user presses push button 31 indicating to increase sound volume of electronic equipment 22 such as an audio system by the thumb of the left hand in a state in which the user holds steering wheel 20. Then, switch 4 at the back side is electrically connected, and a voltage according to resistance values of resistor 23 and resistor 1 is output to drive unit 24 of electronic equipment 22 and control unit 7 of input device 10.
A case in which, for example, power supply voltage V0 is 5V and each of the resistance values of resistor 23 and resistors 1 to 3 is 1 kΩ is as follows. An output voltage of 2.5 V is output to drive unit 24 and control unit 7. This value of the output voltage is obtained by multiplying 0.5, which is a value obtained by dividing the resistance value of 1 kΩ of resistor 1 by the sum of the resistance values of 2 kΩ of resistor 23 and resistor 1, by power supply voltage V0 of 5V. Thus, drive unit 24 detects that push button 31 is pressed and controls the equipment, so that the sound volume of electronic equipment 22 is increased.
At the same time, control unit 7 detects from the output voltage of 2.5 V that push button 31 is pressed, and outputs a predetermined output signal from output terminal 9 to display device 26. A plurality of push buttons 31 to 33 and push buttons 41 to 43 are displayed on display device 26, and the pressed push button 31 among the push buttons is displayed in such a manner that black and white are reversed.
On the other hand, when push button 32 indicating to reduce sound volume is pressed, switch 5 is electrically connected. Then, an output voltage of 3.35 V is output. This value is obtained by multiplying 0.67, which is a value obtained by dividing the sum of the resistance values of 2 kΩ of resistors 1 and 2 by the sum of the resistance values of 3 kΩ of resistor 23 and resistors 1 and 2, by power supply voltage V0 of 5V. As a result, the sound volume of electronic equipment 22 is reduced, and push button 32 on display device 26 is displayed in such a manner that black and white are reversed.
Alternatively, when push button 33 showing a mode to change a supply source of music, for example, from a disk to radio is pressed, switch 6 is electrically connected. Then, an output voltage of 3.75 V is output to drive unit 24 and control unit 7. This value of the output voltage is obtained by multiplying 0.75, which is a value obtained by dividing the sum of the resistance values of 3 kΩ of resistors 1 to 3 by the sum of the resistance values of 4 kΩ of resistor 23 and resistors 1 to 3, by power supply voltage V0 of 5V.
Furthermore, when a user presses push button 41 or 42 indicating to increase or decrease a temperature of electronic equipment 22A such as an air conditioner by the thumb of the right hand, switch 4A or switch 5A at the back side is electrically connected. Then, a voltage according to resistance values of resistor 23A and resistors 1A and 2A is output to drive unit 24A and control unit 7. As a result, the temperature of electronic equipment 22A is increased or decreased, and push button 41 or 42 displayed on display device 26 is displayed in such a manner that black and white are reversed.
Furthermore, when push button 43 for changing on/off of ventilation is pressed, switch 6A is electrically connected. Then, an output voltage of 3.75 V is output to drive unit 24A and control unit 7. This value of the output voltage is obtained by multiplying 0.75, which is a value obtained by dividing the sum of the resistance values of 3 kΩ of resistors 1A to 3A by the sum of the resistance values of 4 kΩ of resistors 23A and resistors 1A to 3A, by power supply voltage V0 of 5V.
That is to say, input device 10 is mounted on steering wheel 20, and any of push buttons 31 to 33 and push buttons 41 to 43 is operated by stretching, for example, only the thumb without taking hand off steering wheel 20. Thereby, the sound volume of electronic equipment 22 or the temperature of electronic equipment 22A in a vehicle can be controlled. That is to say, a user can easily control the equipment during driving a vehicle.
Furthermore, control unit 7 previously stores output voltage values according to the operation of each switch, that is, the output voltage of 2.5 V when switch 4 is operated, the output voltage of 3.35 V when switch 5 is operated, and the output voltage of 3.75 V when switch 6 is operated. Then, control unit 7 detects which switch is operated from the output voltage when a switch is operated, and allows the operated push button among push buttons 31 to 33 and push buttons 41 to 43 to be displayed on display device 26 in such a manner that black and white are reversed. Therefore, a user can do reliable operation without error.
However, due to variation of the resistance values of diodes 25 and 25A, a voltage drop of about 0.5 V to 1 V may occur in applied voltage V1 applied to input terminal 8. In this case, an output voltage varies.
A case in which a voltage drop by diodes 25 and 25A occurs is described. For example, a case in which applied voltage V1 applied to input terminal 8 is 4.5 V by the voltage drop by diode 25 is as follows. Herein, applied voltage V1 is a voltage that is applied to input terminal 8 when all switches are turned off. The output voltage when push button 32 is pressed and switch 5 is electrically connected is 3.00 V. This value of the output voltage is obtained by multiplying 0.67, which is a value obtained by dividing the sum of the resistance values of 2 kΩ of resistors 1 and 2 by the sum of resistance values of 3 kΩ of resistor 23 and resistors 1 and 2, by applied voltage V1 of 4.5V.
On the other hand, a case in which applied voltage V1 is 4 V by diode 25 is as follows. The output voltage when push button 33 is operated and switch 6 is electrically connected is 3.00 V. This value of the output voltage is obtained by multiplying 0.75, which is a value obtained by dividing the sum of the resistance values of 3 kΩ of resistors 1, 2 and 3 by the sum of resistance values of 4 kΩ of resistor 23 and resistors 1 to 3, by applied voltage V1 of 4V. As a result, this output voltage is the same value as that when the above-mentioned switch 5 is electrically connected.
More specifically, the output voltages when pressed switches 4, 5, and 6 are vary for each equipment by a voltage drop due to variation of the resistance value of diode 25 for each equipment. Therefore, in an input device having a plurality of switches, the operated switch may not be able to be detected.
That is to say, in a conventional input device, control unit 7 previously stores output voltage values according to the operation of each switch, and detects which switch is operated based on the stored values. Therefore, in a case where an output voltage changes due to the voltage drop by variation of the resistance values of diodes 25 and 25A for each equipment when a switch is operated, the operated switch may be detected wrongly. As a result, it is difficult to obtain an input device provided with a large number of switches and capable of carrying out a variety of operations accurately.